Enzymatic breakdown

In a recycling system, the aqueous discharge effluent from both centrifiiges is returned to the extractors for additional oil recovery, the water being reused. During this extraction process the viscosity of the emulsions increases because peel polysaccharides, mainly pectins, are transported with the emulsion. Enzymatic breakdown of the internal links of the pectin, catalysed by endopolygalacturonase activity, produces an important decrease in the viscosity of the emulsion [16]. In addition, enzymatic treatment removes pectins from the emulsion and contributes to it destabilization [17]. 

Nyns EJ, D Zach, EE Snell (1969) The bacterial oxidation of vitamin Bg. Vlll. Enzymatic breakdown of a-(iV-acetylaminomethylene)succinic acid. J Biol Chem 244 2601-2605. 

The sinusoids transport both portal and arterial blood to the hepatocytes. The systemic blood delivered to the liver contains nutrients, drugs, and ingested toxins. The liver processes the nutrients (carbohydrates, proteins, lipids, vitamins, and minerals) for either immediate use or for storage, while the drugs and toxins are metabolized through a variety of processes known as first-pass metabolism. The liver also processes metabolic waste products for excretion. In cirrhosis, bilirubin (from the enzymatic breakdown of heme) can accumulate this causes jaundice (yellowing of the skin), scleral icterus (yellowing of the sclera), and tea-colored urine (urinary bilirubin excretion). 

Note The role of lingual lipase in the digestion of dietary lipids is minor because it accounts for less than 10% of the enzymatic breakdown of triglycerides. 

As discussed in previous sections, sugars, starch and (ligno)cellulose can be converted into ethanol by fermentation, the latter via preliminary chemical and physical pretreatment followed by enzymatic breakdown of the biopolymers. Pure ethanol can be added to gasoline or diesel. However, this requires an energy-intensive distillation step. This and the energy used in fertilizers, transportation... 

A synaptic neurotransmitter may become inactivated by several mechanisms. It may passively diffuse out of the synapse it may undergo enzymatic breakdown it may be taken up into a cell through a selective reuptake pump and, intracellularly, it may be taken back into a vesicle for future release, or it may be converted enzymatically. 

Intracellular messengers A biphasic effect of ginkgo extract is seen on cAMP phosphodiesterase under in vitro and ex vivo conditions (Saponara and Bosisio 1998 Macovschi et al. 1987). Whereas low concentrations (0.25-4.0 mg/L) activate the enzyme, higher concentrations (5-250 mg/L), dose-dependently inhibit it. However, tolerance develops to this effect because it is undetectable after daily administration for 4 days. Thus, ginkgo may initially produce effects by inhibiting enzymatic breakdown of cAMP. This mechanism is similar to the stimulant caffeine, but it is not likely to explain any long-term effects of ginkgo because it disappears after chronic daily treatment. The responsible constituent for this effect has not been identified. 

Most components of food (see p. 360) cannot be resorbed directly by the organism. It is only after they have been broken down into smaller molecules that the organism can take up the essential nutrients. Digestion refers to the mechanical and enzymatic breakdown of food and the resorption of the resulting products. 

Bioactivation is a classic toxicity mechanism where the functional group or the chemical structure of the drug molecule is altered by enzymatic reactions. For example, the enzymatic breakdown of the analgesic acetaminophen (paracetamol), where the aromatic nature and the hydroxyl functionality in paracetamol are lost, yields A -acetyl-p-benzoquinone imine, a hepatotoxic agent. Paracetamol can cause liver damage and even liver failure, especially when combined with alcohol. 

Surface lipids of plants. The thick cuticle (Fig. 1-6) that covers the outer surfaces of green plants consists largely of waxes and other lipids but also contains a complex polymeric matrix of cutin (stems and leaves) or suberin (roots and wound surfaces).135/135a Plant waxes commonly have C10 - C30 chains in both acid and alcohol components. Methyl branches are frequently present. A major function of the waxes is to inhibit evaporation of water and to protect the outer cell layer. In addition, the methyl branched components may inhibit enzymatic breakdown by microbes. Free fatty acids, free alcohols, aldehydes, ketones, 13-dike tones, and alkanes are also present in plant surface waxes. Chain lengths are usually C20 - C35.136 Hydrocarbon formation can occur in other parts of a plant as well as in the cuticle. Thus, normal heptane constitutes up to 98% of the volatile portion of the turpentine of Pin us jeffreyi.81... 

Glutamate removal. Glutamate s actions ate stopped not by enzymatic breakdown, as in other neurotransmitter systems, but by removal by two transport pumps. The first of these pumps is a presynaptic glutamate transporter, which works as do all the other neurotransmitter transporters already discussed for monoamine neurotransmitter systems such as dopamine, norepinephrine, and serotonin. The second transport pump, located on nearby glia, removes glutamate from the synapse and terminates its actions there. Glutamate removal is summarized in Figure 10—22. 

Starch Liquefaction. Starch in its natural state is only degraded slowly by CC-amylases. To make the starch susceptible to enzymatic breakdown, it is necessary to gelatinize and liquefy a slurry with a 30—40% dry matter content. Gelatinization temperature depends on the type of starch (67) com is the most common source of industrial starches followed by wheat, tapioca, and potatoes. Liquefaction is achieved by adding a heat-stable a-amylase to the starch slurry. The equipment used for liquefaction may be stirred tank reactors, continuous stirred tank reactors (CSTR), or a jet cooker. Most starch processing plants liquefy the starch with a single enzyme dose in a process using a jet cooker (Fig. 9). 

Degradation. Some synapses rely primarily on the enzymatic breakdown of the released transmitter to terminate synaptic activity. Inhibition of the enzyme responsible for terminating the transmitter allows more of the active transmitter to remain in the synaptic cleft, thereby increasing activity at the synapse. An example is using a drug that inhibits the cholinesterase... 

A G4 PAMAM dendrimer conjugate80 (Fig. 16) has been synthesized, and in vivo studies have demonstrated its ability to protect against experimental infection by influenza A X-31 H3N2 virus in mice. In this case the glycodendrimer not only showed increased binding affinity due to the multivalency, but also facilitated the delivery of sialic acid, preventing enzymatic breakdown in vivo, and diminishing the cytotoxicity. 

Process (e.g., enzymatic breakdown) whereby an organic compound is transformed to a simpler carbon entity (e.g., glucose to carbon dioxide). Volume 2(1,7). 

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